Sen. John McCain underwent surgery to remove a blood clot above his left eye and will stay in Arizona to recover next week – denying Republicans a key vote in their push to repeal Obamacare, where the GOP already has no room for error.

Republican leaders want to hold a procedural vote to launch debate on its health care plan next week, with Senate Majority Whip John Cornyn telling the Associated Press that he expected the chamber to vote to take up its bill on “Tuesday night or Wednesday at the latest.”

But McCain’s (R-Ariz.) absence from the Senate significantly complicates those plans. Two GOP opponents of the Obamacare repeal bill – Sens. Susan Collins of Maine and Rand Paul of Kentucky – have already said they will not vote to proceed to the measure. That means Republicans, who holds 52 votes in the Senate, already could not afford to lose any other GOP senator for the procedural vote.

Senate Majority Leader Mitch McConnell (R-Ky.) said on Saturday night that the Senate will “defer” consideration of its attempt to repeal and replace Obamacare.

In a statement released by McCain’s office, the Mayo Clinic said surgeons removed a blood clot from above the senator’s left eye during a procedure on Friday at its hospital in Phoenix.

“Senator McCain received excellent treatment at Mayo Clinic Hospital in Phoenix, and appreciates the tremendous professionalism and care by its doctors and staff,” McCain’s office said in a statement Saturday night. “He is in good spirits and recovering comfortably at home with his family. On the advice of his doctors, Senator McCain will be recovering in Arizona next week.”